1. Field of the Invention
The present invention relates to an image processing device and an image processing method.
2. Description of Related Art
Images printed on sheets of paper using conventional printers based on the electronic photograph system have occasionally been found to cause variation in density, as if toner has been swept up. This is because the density of images, containing characters and figures, decreases on the front end side of the sheet-feeding direction, and increases on the rear end side. Mode of density variation characterized by decreased density on the front end side is generally called “front end fading”, and increased density on the rear end side is generally called “sweep-up”.
As a solution for the sweep-up problem, there has been disclosed a method of producing a correction object by which sweep-up is less recognizable (see Japanese Laid-Open Patent Publication No. 2009-58765, for example). According to the method, density in regions where the sweep-up is readily recognizable is adjusted depending on color of the object, angle of outline of the object away from the sheet-feeding direction, and so forth.
In general, images including characters, required to be sharp, are often processed by thinning, for reducing pixel values on the outline of images, or by emphasizing outlines of characters (see Japanese Examined Patent Publication No. 4189467, for example).
Effect of the thinning is, however, not attainable in the swept-up image, since the density of characters increases on the rear end side of the sheet-feeding direction. Conversely, in case of front end fading, the effect of thinning will be excessive since the decreased density by the front end fading is further decreased by the thinning. Accordingly, given that the image per se is originally thin, such image would occasionally fade or disappear due to excessive thinning.
As described in the above, not only thinning, but also correction of sweep-up and front end fading are categorized as the processing of increasing or decreasing pixel values of pixels on the outlines of image, so that it has been difficult to attain both of thinning and correction of sweep-up or the like at the same time.